1. Field of the Invention
This invention relates to a fuel injection valve, more particularly to a fuel injection valve used for an internal combustion engine.
2. Description of the Related Art
Fuel injection valves accelerating atomization of fuel used so far include, for instance, the one disclosed in Japanese Published Unexamined Patent No. 2000-104647. FIG. 13 is a cross-sectional elevation of a fuel injection valve disclosed in that publication, FIG. 14 an enlarged view of the lower end of the fuel injection valve of FIG. 13, and FIG. 15 a view of the bottom of the fuel injection valve of FIG. 14 seen from the direction shown by arrow E in the Figure.
The illustrated fuel injection valve 1 includes an electromagnetic coil 3, a fixed iron core 4 and metal plates 5 defining a magnetic current path, all disposed in a resin housing 2. The electromagnetic coil assembly 3 consists of a resin bobbin 3a, a coil 3b being wound around the outer periphery of the bobbin 3a, and a terminal 6 formed for connecting to an external source of electric power. The resin housing 2 is molded around the electromagnetic coil assembly 3.
An adjuster 8 for adjusting the loads on a compression spring 7 is secured to the inside of the fixed iron core 4. Each of the two metal plates 5 forming a magnetic current path is fixed at one end to the fixed iron core 4 by welding and is welded at the other end to an electromagnetic pipe 9 forming a magnetic current path. A non-magnetic pipe 11 is situated in the space between the fixed iron core 4 and the magnetic pipe 9 and secured thereto in a way enabling a movable iron core 10 situated within the magnetic pipe 9 to move up and down.
A needle pipe 12 is welded and secured to one end of the movable iron core 10. The movable iron core 10 is abutting at the other end (or the end of the needle pipe 12 whereto the movable iron core 10 is secured) against a compression spring 7, and a valve head 101 is fixed as a valve to the other end of the needle pipe 12. The valve head 101 is guided to a valve seat 102 situated within the magnetic pipe 9 and is situated in a seating section 102a of the valve seat 102 in a way enabling its settling in and lifting off the seating section 102a. The outer periphery of the section of the valve head 101 guided by the valve seat 102 is processed into a polygonal shape, thus giving space between a guiding section 102b of the valve seat 102 and the valve head 101 for fuel to flow through. An orifice plate 104 having a plurality of fuel injection orifices 103 is situated at the lower end of the valve seat 102, as well illustrated in FIGS. 14 and 15. Each of the injection orifices 103 is formed to be oblique from axis C of the fuel injection valve at a given angle.
In such conventional fuel injection valves like this, the valve head 101 is moved up and down by an electromagnetic driving means provided by the electromagnetic coil 3, the movable iron core 10 and other members locating upwards to open and close the valve through the settling in and lifting off the valve seat 102 of the valve head 101. Fuel flows through the space between the valve head 101 and the valve seat 102 into a fuel cavity 105 situated beneath the lower end of the valve head 101 and above the orifice plate 104, and then injected out of the injection orifices 103 formed in the orifice plate 104.
The fuel injection valve 1 as shown in FIGS. 13-15 wherein the direction of fuel injection is defined by the angle of inclination of the injection orifices 103 formed in the plate 104 is imperfect in that it is difficult to achieve a satisfactorily large spray angle for the injected fuel because the fuel flowing through the fuel cavity 105 onto the orifice plate 104 generally gathers in the central section from the outer periphery. For achieving a large spray angle (say, 15xc2x0 or more) by using a double-spray type valve it is necessary to form the injection orifices 103 having a large angle of inclination, and it is difficult to form such largely inclined orifices with small diameters, meaning that it is difficult to achieve a satisfactory atomization of fuel for which orifices must have small diameters. If largely inclined orifices with small diameters are successfully formed, the processing of such orifices in the orifice plate will involve a considerable cost. In case of an orifice plate in which more than six injection orifices are to be formed for the acceleration of atomization, it is particularly difficult to form these orifices because their diameters must be reduced further.
Although it is possible to govern the direction of fuel injection and to induce larger spray cone angles by increasing L/xcfx86d, or the ratio of depth L of the injection orifices 103 to be formed in the orifice plate 104 to diameter xcfx86d, or the diameter of the injection orifice, this could result in an impaired atomization. Further, it is difficult to perform the work to form the injection orifices 103 with larger L/xcfx86d values in the orifice plate 104, and the work to form the injection orifices 103 having larger angles of inclination as well involves a significant manufacturing cost increase because it is difficult to form such injection orifices in the orifice plate 104.
Although a fuel injection valve having an orifice plate with a fuel cavity formed wherein has been proposed as described in the Japanese Published Unexamined Patent Application Hei 10-122096, it is difficult to manufacture such an orifice plate, and thus involving a significant manufacturing cost increase.
In fuel injection valves injecting spray flows from a plurality of injection orifices to a plurality of directions, injection orifices are disposed along the circumferences of a plurality of concentric circles as described in Japanese Published Unexamined Patent Application Hei 11-72067. However, such fuel injection valves are imperfect in that they fail to produce spray flows consisting of fuel droplets of uniform size because of an inconsistency in the particle size composition of the fuel flows from the injection orifices disposed along the circumferences between inner and outer circles.
The present invention provides a low-priced and efficient fuel injection valve enabling the production of atomized uniform spray flows at a large spray angle (say, 15xc2x0 and more) as well as the acceleration of atomization of injected fuel and including an orifice plate in which injection orifices are easily formed.
According to one form of the present invention, a fuel injection valve includes an orifice plate having a plurality of (more than six) injection orifices formed therein, a valve seat with a valve seating formed in the upstream section of said injection orifices, a single cylindrical fuel flow path formed in said valve seat, a fuel cavity formed in the space between said fuel flow path and said orifice plate having a plurality of said injection orifices and situated directly above a plurality of said injection orifices, and a valve member supported by said valve seat in a way enabling reciprocations and having an abutting section that can be settled in and lifted off a valve seating formed in said valve seat, and produces a plurality of spray flows consisting of a plurality of fuel flows injected out of injection orifices disposed in said orifice plate, wherein a plurality of injection orifices formed in said orifice plate are disposed only along ØP, or the diameter of a single pitch circle with its center coinciding with the axis of the fuel flow path, and the diameter of the fuel flow path (xcfx86D1), the diameter of each of the injection orifices (xcfx86d), xcfx86P and the depth in the axial direction of the fuel cavity (t) are made have the relationships xcfx86D1+xcfx86d less than xcfx86P and t less than xcfx86d.
In a preferred embodiment, of a plurality of said injection orifices formed in said orifice plate, each group of injection orifices producing a single spray flow is disposed at an equal pitch along the circumference of the pitch circle.
In a preferred embodiment, the angle formed at the fuel injecting side of the orifice plate by the axis of each of the injection orifices disposed in said orifice plate with an imaginary straight line which passes through the center of each of the injection orifices and is parallel to the axis of the fuel injection valve increases with an increase in the distance between each injection orifice and the basic axis which passes through the centre of the orifice plate and crosses at a right angle the radial component of the injecting direction of fuel spray flows in each group of injection orifices producing a single spray flow of a plurality of said injection orifices formed in said orifice plate.
In a preferred embodiment, a plurality of said injection orifices formed in said orifice plate consist of at least two different groups of injection orifices with different diameters in a fuel injection valve wherein xcfx86D1, xcfx86d1 (the diameter of the injection group having the largest diameter), xcfx86P and t are made to have the relationships xcfx86D1+xcfx86d1 less than xcfx86P and t less than xcfx86d1.